The New York Times reported Monday that federal agencies are also looking into the matter. Firms are required to keep their own trading accounts separate from those of their customers.

Mr. Donohue said CME's decision Monday to place a “liquidation only” limit on trades for MF Global customers and to bar MF Global traders and other traders who clear through the firm from the trading floors was taken after a meeting of CME's emergency action committee Monday morning.

MF Global filed for bankruptcy protection Monday.

When Lehman Brothers filed for bankruptcy protection in September 2008, that firm's house positions, or positions owned by the bank as opposed to customers, were sold in an auction to other derivatives trading firms after a meeting of the emergency action committee called for that sale.

Chicago-based Citadel LP and DRW Trading were among the firms invited to place bids in that Lehman auction. DRW ended up purchasing Lehman's foreign exchange, interest-rate derivatives and agricultural derivatives portfolios.

Hundreds of Chicago traders were barred from the floors of the Chicago Board of Trade and Chicago Mercantile Exchange yesterday in the wake of MF Global's bankruptcy filing, traders said.

Some of the pits operated with just half their usual traders, brokers and clerks, lowering liquidity on the trading floors and widening spreads. Still, it didn't have a major impact on overall volume because most trading is done electronically.

CME barred the traders either because they were employees of MF Global or because they were traders who cleared their trades through MF Global or one of its subsidiaries. As a result those MF Global accounts remained mainly locked up Monday unless traders were able to re-margin them and transfer them to another clearing firm.

The less active pits could persist most of the week because independent traders who were shut out must find new clearing firms to back their trades. A trickle of the traders returned Monday, but most were still seeking new firms, traders said.